1. Field of the Invention
The present invention relates to an elastic wave device used for a resonator, a band-pass filter, or the like and to a method for manufacturing the elastic wave device. In more particular, the present invention relates to an elastic wave device in which a first multilayer metal film and a second multilayer metal film are formed on a piezoelectric substrate and to a method for manufacturing the elastic wave device.
2. Description of the Related Art
In a conventional device, with the reduction in size of a mobile phone or the like, the reduction in size of a band-pass filter used therefor is also required. As this type of band-pass filter, an elastic wave device using an elastic wave, such as a surface acoustic wave, has been widely used.
Japanese Patent No. 5131117 discloses one example of the elastic wave device. In the elastic wave device disclosed in Japanese Patent No. 5131117, on a LiTaO3 substrate 100, a second electrode 121 is laminated so as to be overlapped with a part of a first electrode 111 including an IDT electrode. The first electrode 111 and the second electrode 121 are each formed of a multilayer metal film. In the first electrode 111, a Pt film 113, a Ti film 114, and an AlCu film 115 are laminated in this order on a NiCr film 112, and on the AlCu film 115, a Ti film 116 is laminated. The bottommost film of the multilayer metal film forming the second electrode 121 is formed of a Ti film 122.
Japanese Patent No. 5131117 discloses that since the Ti film of the first electrode and the Ti film of the second electrode are in contact with each other, the contact resistance therebetween can be decreased.
In addition, according to a surface acoustic wave device disclosed in International Publication No. WO 09/150786, an electrode is formed of a multilayer metal film including an AlCu epitaxial film and a Ti film laminated thereon. In this surface acoustic wave device, it has been disclosed that since hillocks of Cu are generated when the multilayer metal film as described above is exposed to a high temperature, a low temperature treatment is necessarily performed.
With the reduction in size of the elastic wave device, improvement in electric power handling capability thereof has been strongly required. According to the elastic wave device disclosed in Japanese Patent No. 5131117, although the contact resistance described above could be decreased, the electric power handling capability was not sufficient.
In addition, although International Publication No. WO 09/150786 has disclosed the surface acoustic wave device using the multilayer metal film including an AlCu epitaxial film, the contact resistance and the electric power handling capability of the structure in which multilayer metal films are laminated to each other have not been discussed.